linux-kernel - Re: [PATCH V2 03/27] mmc: mmci: convert dma

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Message-ID: <55622e1c-190f-6903-ab04-16089264f277@linaro.org>
Date:   Thu, 27 Sep 2018 09:55:05 +0100
From:   Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
To:     Ulf Hansson <ulf.hansson@...aro.org>,
        Ludovic Barre <ludovic.Barre@...com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre Torgue <alexandre.torgue@...com>,
        Benjamin Gaignard <benjamin.gaignard@...aro.org>,
        Gerald Baeza <gerald.baeza@...com>,
        Loic Pallardy <loic.pallardy@...com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        DTML <devicetree@...r.kernel.org>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        linux-stm32@...md-mailman.stormreply.com
Subject: Re: [PATCH V2 03/27] mmc: mmci: convert dma_setup callback to return
 an int

Thanks for looping me!

On 24/09/18 15:28, Ulf Hansson wrote:
>>   /* Initialize the dml hardware connected to SD Card controller */
>> -static void qcom_dma_setup(struct mmci_host *host)
>> +static int qcom_dma_setup(struct mmci_host *host)
>>   {
>>          u32 config;
>>          void __iomem *base;
>> @@ -131,7 +131,7 @@ static void qcom_dma_setup(struct mmci_host *host)
>>
>>          if (producer_id < 0 || consumer_id < 0) {
>>                  host->variant->qcom_dml = false;
> It seems like the existing code is an attempt to fallback to use pio
> mode. However, I doubt it works as is.

If I remember it correctly, Yes, that was the intent. we should still be 
able to use the pio mode if the dma setup fails.

I believe pio mode should work, Last time when I tried (3-4 years back) 
it did work!

> 
>> -               return;
>> +               return -EINVAL;
> My point is, if you return an error code here, it means that the error
> code becomes propagated and ->probe() will fail.
That would be very bad!, We should report it and may be just continue 
with pio mode.

> 
> Ideally, we should be able fall back to pio mode when dma doesn't
> work. I have looped in Srinivas who implemented the qcom dml support,
> let's see if he can explains the intent with the code.
> 
> I also volunteer to help out running some tests on the 410c platform,
I think you meant IFC6410.. DB410c uses sdhci.


--srini
> however allow me a day or two to do that.
>